Common mistakes
- J-channel with no head flashing above
- Caulk relied on as the primary seal
- Cut siding tight with no drainage path
- Reusing rotten sill trim behind new channel
Right sequence
Wrap and flash the opening, set the window or integrate existing unit, then J-channel and siding.
Pairing windows with siding is the cleanest time to rebuild openings.
Repair note
Localized channel replacement can help cosmetics. Soft sheathing behind means a larger scope.